The present invention relates to an improvement in a walk behind self-propelled crawler snowplow equipped with a snowplow mechanism having an auger and a blower.
Walk behind self-propelled crawler snowplow machines equipped with an auger and a blower are known as disclosed, for example, in Japanese Utility Model Publication No. (SHO) 51-34111.
The disclosed snowplow machine includes a belt drive power transmission system having a driving pulley connected to the output shaft of an engine, a driven pulley connected to one end of a rotating shaft, and an endless belt trained around the driving and driven pulleys for transmitting power from the engine to the rotating shaft, so that an auger and a blower connected to the rotating shaft are driven in rotation by the engine power. In operation, the auger rotates to cut snow away from a road, for example, and feed a cut mass of snow to the blower which rotates to blow out the snow through a discharge duct to a place distant from the snowplow machine. The snow on the road is thus removed.
During the snow plowing operation, the auger may be subjected to a momentary overload when interference occurs between the auger and a rock or other object projecting from the road surface. The auger may be also subjected to a continuous overload when foreign matter, such as a stone, wood piece or block of ice, is caught between an auger case and the auger. Under such overloaded condition, the auger is forcibly stopped from rotating and an excessively large torque is developed in a drive unit (including the engine and the power transmission system). To withstand such a large torque, the drive unit requires extensive strengthening of its structural components, which incur additional cost.
According to one prior improvement shown in Japanese Utility Model Laid-open Publication No. (SHO) 50-14720, shear bolts are used to mount the auger to the rotating shaft. When the auger is subjected to an overload during snow removing operation, the shear bolts are broken to thereby separate the connection between the auger and the rotating shaft, allowing the rotating shaft to further continue rotation alone.
In order to restart the snow removing operation, the broken shear bolts must be replaced with new ones. However, since the shear bolts are located at a radial inward position of auger blades which is relatively uneasy to access, shear bolt replacement is tedious and time-consuming. This leads to a relatively long downtime of the snowplow machine and a reduced efficiency of the snow removing operation.
It is accordingly an object of the present invention to provide a walk behind self-propelled crawler snowplow which is capable of achieving snow removing operation with improved efficiency.
To achieve the foregoing object, according to the present invention, there is provided a walk behind self-propelled crawler snowplow comprising a snowplow mechanism having a rotating shaft, an auger and a blower that are connected in driven relation to the rotating shaft, an engine for driving the snowplow mechanism, a belt drive power transmission mechanism for transmitting rotational power from the engine to the rotating shaft, the power transmission mechanism having a driving pulley releasably coupled with an output shaft of the engine, an electromagnetic clutch adapted to be engaged and disengaged for connecting and disconnecting the engine output shaft and the driving pulley, a driven pulley connected to the rotating shaft, and an endless drive belt trained around the driving and driven pulleys, and an overload protection device associated with the belt drive power transmission mechanism for protecting the engine against overload.
In one preferred form of the present invention, the overload protection device comprises a tension sensor for detecting a tension in the endless belt and generating an electric overload signal to disengage the electromagnetic clutch when a belt tension greater than a predetermined value is detected.
Preferably, the tension sensor comprises a tension roller, a bias means for urging the tension roller against an outer circumferential surface of the endless belt to cause a tension run of the belt to flex inwardly, and a detector unit for detecting tautness of the belt associated with an overload condition by detecting displacement of the tension roller in a direction outward of the endless belt when the tension run of the belt is stretched substantially due an overload acting on the snowplow mechanism.
The tension sensor may further include a pivotally movable lever having one end on which the tension roller is rotatably mounted, the detector unit including an electric switch electrically connected with the electromagnetic clutch and having an actuator held in contact with the opposite end of the lever, the actuator being movable in response to pivotal movement of the lever to turn on and off the switch.
The above and other objects, features and advantages of the present invention will become manifest to those versed in the art upon making reference to the following description and accompanying sheets of drawings in which a certain preferred structural embodiment incorporating the principle of the invention is shown by way of illustrative example.